The long-term theme of this program is the study of the nature of certain types of medical knowledge; and its transformation in to symbolic data structures that can be used by a computer for symbolic reasoning on problems of medical science and medical practice. Such knowledge is partly "fact" and partly "heuristic" (i.e. the knowldge of good judgment, the expertise, the "lore"). The heuristic knowledge is essential for adequate performance. Yet such knowledge is rarely discussed or written about, rarely subject to public or scientific scrutiny, rarely taught in schools (except in apprenticeship programs like internships), and almost never available in libraries. The scientific work that we are pursuing in this program aspires to change this situation - to develop the scientific understanding and tools that will allow rapid explication and use of the heuristic as well as the factual knowledge of fields of science and medicine. In one project, we are studying medical knowledge by intensive study of a real clinical situation - the Stanford outpatient oncology clinic. An interactive consultation system is being developed as a "laboratory" for the work. In another project, software packages are being developed to facilitate the acquisition, representation, and use of medical knowledge by computer programs. In a core research project, a set of concepts for more flexible and general representation of knowledge, known collectively as RLL (Representation Language Language), is being explored.